Skype and similar services have brought the world free calls from computer to computer and cheap calls from computer to phone for those willing to download software and speak while staring at a computer screen.

Now a Swedish start-up called Rebtel is using the same technology, Voice Over Internet Protocol, to bring cheap international calls to cellphones.

It takes a few minutes to set up an account with Rebtel, and users must do it online at the company's Web site. But once done, the service can be used to call any country in the world from any mobile or fixed-line phone in 37 countries, including the United States, Japan and most of Europe.

The mobile and fixed-line numbers of family and friends abroad are entered on the Rebtel Web site, and the company creates a local number that forwards calls to each foreign number.

In addition to a base fee of $1 a week that is charged only for weeks the service is used, Rebtel charges a per-minute fee that varies by country called, usually 2 cents to dial fixed-line phones and about 25 cents for cellphones (though calling a cellphone in the United States costs 2 cents). But even the per-minute cost can be avoided.

For each contact number a customer enters on the Rebtel Web site, the company creates a local phone number the contact can call. So if a Rebtel user in Paris enters on the Web site the cellphone number of a friend in San Francisco, the person in Paris will be given a local number to call, and a San Francisco number the friend can call. To avoid the per- minute cost, the customer in Paris calls his or her local number, the person in San Francisco answers, then hangs up and calls back his local number.

"Now you can make cheap calls from the beach and not just from in front of your computer," said Hjalmar Winbladh, Rebtel's co- founder, chief executive and a self- declared "serial entrepreneur" who sold his previous start-up to Microsoft.

Winbladh and Jonas Lindroth founded Rebtel in January, though they had been working on the idea for about a year before that. Services were first offered in July for a trial period and then officially started in September.

Winbladh declined to provide sales or profit targets. Since initially signing up customers in 35 countries, Rebtel has added 2 and plans to include 10 more by year-end.

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"For us, getting $1 a week for unlimited calls is a good business, but for somebody like T-Mobile, it's bad business because of all the costs the company has," Winbladh said. "We are an organization with 20 people - our entire cost base is probably less than what it costs T-Mobile to run the reception in their headquarters."

With $20 million in financing raised last week, Winbladh, 37, said Rebtel now had the money needed to get the company to profitability. Index Ventures and Benchmark Capital each invested $10 million in Rebtel, money that will be used to expand to more countries, develop new services and pay for marketing.

"We look to invest in businesses that explode traditional ways of doing things by coming up with a better product," said Danny Rimer, a general partner at Index, which also invested in Skype and sold its stake when eBay bought the company last year.

Rimer and Winbladh declined to say what percentage stake Index received in Rebtel for $10 million.

"We don't think this will be any more successful than other new services where you have to do several steps to make a phone call," said Klaus Czerwinski, a spokesman for T-Mobile. "People prefer simplicity."

Mobile phone companies already use Voice Over Internet Protocol, or VOIP, to lower prices and keep customers. Though their services are more expensive than Rebtel's, and in most cases the user must have special software on the mobile phone, analysts say they expect the prices to fall and the services to be simplified.

Since Rebtel customers pay local rates to call abroad, Rimer and Winbladh said the success of the company was at least partly linked to increased use of calling plans in which people pay a flat rate for a large or unlimited bucket of minutes.

Such plans are prevalent in the United States but not in Europe or Asia, where per-minute calling plans dominate.

"We certainly have done quite a bit of analysis," Rimer said, "and we think bucket plans are the inevitable relationship that will develop between mobile phone companies and their customers in the next few years."